While the art is replete with numerous types of pressurized-fluid dispensing apparatus, systems and machines, including those for the above and other viscous fluids, and for a myriad of different uses and applications, many employ cylindrical chamber piston-activated pumps for enabling the microprocessor-controlled pressurized dispensing of fluid that is filled into and then dispensed from the volume of the piston chambers. In view of the limited volume of such piston chambers, however, pairs of such pumps or dual or double-acting pumps have been employed with valving techniques for switching from an emptied piston-pump chamber to an adjacent filled pump chamber for fluid dispensing through a common static mixer or other dispensing head. A typical system of this type is the 2500 series double-acting dispensers of Ashley Cross Company of Newburyport, Mass. and similar resin-dispensing systems of others wherein when one piston pump empties, the other is switched to the dispensing head to continue the fluid dispensing while the emptied piston chamber is re-filled with fluid.
Unfortunately, for some applications, however, where strict uniformity of the dispensed fluid is essential, as, for example, in laying down a uniform sealing bead as for adhering a gasket or the like, the switching from one dispensing pump to the second usually involves an interruption in the dispensed fluid flow, or at least a marked variation in its deposit—generally, quite abrupt stopping during the transfer—that forbids the laying down of a constant-dimension bead throughout.
It is to the solution of this problem and other related difficulties with such prior art piston pump dispensing systems that the present invention is primarily directed, the invention providing for constant velocity of fluid dispensing flow throughout the alternate dispensing and filling of the pairs of piston pump chambers, including during the switching between them.